Re: What is an acceptable velocity spread.....
Just like with any other set of statistics, it all depends on the sample size. Some guys at my local range will chrono 5-10 rounds and make their decisions based on that small sample (they don't want to shoot out their barrels in testing you know).
I prefer first shoot my workup loads for group size at the range I intend to use them for. The load yielding the best group is then loaded up for some serious chrono testing. At least 25 and as many as 50 rounds are then shot and chronograph'd. It's amazing how revealing large sample sizes can be. If you want, you can also use "Olympic Scoring" and throw out the one or two highest speed and one or two lowest speed, rounds. It's just like a group when testing. If you have 4 out of 5 in one hole and the 5th goes wandering, it's a flier and therefore an anomaly.
I'm more interested in average speed and Mean Absolute Deviation than whether I had one extremely high or low speed round.
Once you have a nice consistent, and accurate load, pay more attention to case prep steps like flash hole de-burring, neck turning, annealing, and bullet seating pressures. It's usually easy for one to feel a case that takes a great deal more or less pressure to seat a round. Those go into the "fouler" or "produce shooting" (canteloupe, coconut, pineapple, apples, oranges, etc) sessions at the local gravel pit.
Also, don't assume that a load thrown from that good old "Famous" powder measure is always consistent. Sometimes a good accurate scale, used for every load, can make a difference in "spreads" on either the target or the chronograph.
Just don't rely on small sample sizes.
